The present invention relates to a pump. More particularly this invention concerns a magnetically coupled and self-lubricated can-type pump.
A standard magnetically coupled can-type pump has a housing plate having a front face and a back face, a can fixed to the plate and defining a chamber on the back face thereof, and a bearing sleeve in the can fixed to the plate and extending rearward from the back face thereof along an axis. A rotor shaft extending axially through the sleeve is supported by bearings in the sleeve for rotation therein about the axis. An impeller is provided on a front end of the rotor shaft in a pump chamber at the front face of the housing plate. A rotor body fixed to a rear end of the shaft extends axially forward in the can around the bearing sleeve. It carries a plurality of permanent magnets that coact with another rotor or stator outside the can to rotate the impeller.
No electricity flows in the rotor of the pump to create a shock hazard so that it can run wet. The interior of the can is filled with the liquid being moved by the pump, for instance coolant water or lubricating oil. The rotor body is formed with one or more axially throughgoing passages and radially extending vanes are provided on the rear end of the rotor body. As the rotor spins, the vanes project fluid outward, pulling more axially in through the rotor body and thereby cooling and/or lubricating it and its bearings.
Such radial vanes have only limited pumping capacity at high pressure. Making them bigger, while it increases the volume of liquid moved, increases the amount of cavitation and the load on the rotor, decreasing pump efficiency. Furthermore the liquid is moved most forcibly between the rear end of the pump and the can, not in the central region of the body where such movement is most needed.
When the bearings are not adequately cooled and/or lubricated, they can burn out. Such failure, if not detected, can lead to offcenter rotation of the rotor so that it comes in contact with the can and destroys the entire pump.
It is therefore an object of the present invention to provide an improved magnetically coupled rotary canned pump.
Another object is the provision of such an improved magnetically coupled rotary canned pump which overcomes the above-given disadvantages, that is which ensures good pumping of the coolant/lubricant through the rotor.
A further object is to provide a pump that is not liable to bearing burnout and the typically following catastrophic failure.
A pump has according to the invention a housing plate having a front face and a back face, a housing can fixed to the plate and defining a chamber on the back face thereof, a bearing sleeve in the can fixed to the plate and extending rearward from the back face thereof along an axis, and a rotor shaft extending axially through the sleeve and having a front end and a rear end. Bearings support the rotor shaft in the sleeve for rotation therein about the axis. The shaft has an outer surface spaced a predetermined inner radial distance from an inside surface of the bearing sleeve. An impeller is carried on the rotor-shaft front end in a pump chamber at the front face of the housing plate. A rotor body fixed to the shaft rear end extends axially forward in the can around the bearing sleeve. The rotor body has an outer surface spaced a predetermined outer radial distance from an inside surface of the can. The inner radial distance is substantially smaller than the outer radial distance.
Thus with this system if one of the bearings fails, the maximum the rotor can move radially is the small radial distance, so the outside of the rotor cannot contact the inside of the can. Substantial damage to the pump is thus avoided since the external stator and can remain perfectly preserved. If the bearings are carried according to the invention in removable rings set in the rotor body, they can be replaced with these rings so that the rotor body itself is preserved.
According to the invention at least one temperature sensor is provided adjacent one of the bearings for detecting bearing failure. This sensor is connected to a controller having, in turn, means for making a visible or acoustic alarm to indicate this early stage of bearing failure when friction causes heating.
An electric motor in accordance with the invention that is magnetically coupled to the rotor rotates same about the axis. The controller detects excessive current consumption of the motor and thereby detects bearing failure. This is a second way of averting catastrophic failure by sensing early signs of bearing failure, namely friction causes an increase in the load on the drive motor.
The pump according to the invention has a vane on the rotor for pumping liquid from inside the can axially through the bearings on rotation of the rotor about the axis.
According to another aspect of the invention the rotor body has an outer surface confronting an inner surface of the bearing sleeve and defining therewith an annular and axially extending space. One of the surfaces is formed with a helicoidal groove open toward the other of the faces. When the body rotates relative to the bearing sleeve, the groove pumps liquid axially through the bearing.
There are two such bearings spaced axially on the shaft. The rotor body is formed at each of the sleeves with the groove. In addition the groove, which is typically formed in the rotor body, has an axial outer end open outside the sleeve and an axially inner end open inside the sleeve.